With the demand on a high-speed, large-volume data communication system for processing and transmitting a variety of information such as radio data as well as providing voice-oriented services, there is a need for developing a technique for transmitting large-volume data through the wireless communication network whose capacity is similar to that of the wired communication network. Therefore, an error handling method is essential for minimizing data loss and for increasing system transmission efficiency.
Examples of the error handling method include a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the FEC scheme, a receiver corrects an error by appending an extra error correction code to information bits. In the ARQ scheme, when a received signal has an error, a transmitter corrects the error by retransmitting data. A hybrid ARQ (HARQ) scheme is a combination of the FEC scheme and the ARQ scheme.
According to the HARQ scheme, the receiver basically attempts error correction when data is received, and determines data retransmission by using an error detection code. For error detection, the transmitter can append a cyclic redundancy check (CRC) as the error detection code to the data to be transmitted. The receiver can detect an error of the received data by using the appended CRC. If no error is detected by the receiver by using the CRC, the receiver feeds back an acknowledgement (ACK) signal as a response signal to the transmitter. Otherwise, upon detecting an error from the received data, the receiver transmits a negative-acknowledgement (NACK) signal as a response signal to the transmitter. That is, the ACK/NACK signal is feedback on successful or unsuccessful reception of uplink data. The transmitter retransmits data upon receiving the NACK signal. Such a HARQ operation is performed in a physical layer.
The HARQ operation is performed by at least one HARQ entity included in a user equipment (UE) or a base station (BS). The HARQ entity allows continuous data transmission while waiting for the feedback (i.e., the ACK signal or the NACK signal) on successful or unsuccessful reception of previous data transmission. In an uplink scenario, the UE receives resource assignment information from the BS, and when the UE transmits associated HARQ information to the HARQ entity, the HARQ entity performs a HARQ process indicated by the HARQ information. To support the HARQ entity, the UE may operate a plurality of parallel HARQ processes.
Hereinafter, a downlink denotes a communication link from the BS to the UE, and an uplink denotes a communication link from the UE to the BS. The uplink transmission and the HARQ operation are performed in the following manner. The BS transmits scheduling information to the UE through a physical downlink control channel (PDCCH) that is a downlink control channel. Then, according to the scheduling information, the UE transmits data to the BS through a physical uplink shared channel (PUSCH) that is an uplink data channel. When the UE transmits the data to the BS, the BS transmits an ACK/NACK signal to the UE through an ACK/NACK channel (i.e., a physical HARQ indicator channel (PHICH)).
If an error occurs in the ACK/NACK channel, the NACK signal may be erroneously transmitted instead of the ACK signal or vice versa. In this case, the UE cannot properly perform retransmission or new transmission. In addition, if an error occurs in the PDCCH, the UE cannot know scheduling information and thus cannot properly perform uplink transmission. As such, a control channel error results in retransmission of unnecessary data or non-transmission of necessary data, which leads to performance deterioration in data transmission.
Accordingly, there is a need for a data transmission method using HARQ considering control channel errors.